GOALS: To evaluate the efficacy and gastrointestinal safety of nabumetone and diclofenac in the treatment of elderly patients with osteoarthritis, participating in a 3-month efficacy trial. BACKGROUND: Elderly patients have an elevated risk for developing gastrointestinal complications with chronic use of nonsteroidal anti-inflammatory drugs. STUDY: This was a randomized, double-blind, parallel-group, multicenter study with a 3-to 14-day placebo washout period and a 12-week active treatment phase. Patients 65 years or older with moderate-to-severe osteoarthritis of the knee or hip were randomized to receive 1,000 to 2,000 mg/d of nabumetone or 100 to 150 mg/d of diclofenac. The primary efficacy parameters were the percent of patients improved using a Patients' and Physicians' Global Assessment at endpoint. Gastrointestinal safety was assessed by the incidence of gastrointestinal symptoms and adverse events. RESULTS: Three hundred thirty-five patients (mean age = 72 years) with active osteoarthritis were enrolled. There were no statistically significant differences between the two treatment groups in any of the primary efficacy variables. However, differences between the groups were apparent in the frequency of adverse gastrointestinal events. Two patients in the diclofenac group had evidence of gastrointestinal bleeding and/or ulcer compared with none in the nabumetone group. In addition, significantly more (p < 0.05) patients (4%) receiving diclofenac had alanine transaminase values more than twice the upper limit of normal at endpoint compared with patients receiving nabumetone (0%). CONCLUSIONS: Nabumetone was as effective as diclofenac in the treatment of elderly patients with moderate-to-severe osteoarthritis. However, the gastrointestinal safety profile of nabumetone was superior to that of diclofenac with respect to elevation of liver enzymes.